A number of advanced energy storing device technologies have recently been developed, such as metal hydride (e.g., Ni--MH), lithium-ion, and lithium polymer cell technologies, which promise to provide high energy generation for a wide range of commercial and consumer applications. In high-energy applications, a substantial number of individual energy storing devices or cells are typically connected in series and parallel to produce higher voltages and current, respectively. Combining cells in this fashion increases the power capacity of the energy storing system. By way of example, it is believed that a battery system suitable for powering an electric vehicle will likely have a voltage rating on the order of several hundred volts, and a current rating on the order of several hundred amperes (A).
One approach to designing a high-power battery system involves connecting a number of self-contained energy storing devices together in a prescribed series and/or parallel arrangement to achieve a desired voltage and current rating. Using a modular approach in the construction of large battery systems generally provides for increased design flexibility and system maintainability. It can be appreciated, however, that increasing the number of individual energy storing devices within a given battery system increases the difficulty of determining the operating status of each device. The difficulty of detecting existing or imminent faults within the battery system and remedying such faults is also increased.
In a distributed battery system comprising several series connected energy storing modules each containing a number of electrochemical cells, for example, it is considered desirable to use cells which are equivalent or very similar in terms of electrochemistry and voltage/current characteristics. It is known that undesirable consequences often result during charging and discharging when an energy storage cell within a series string of cells exhibits characteristics that vary significantly from those of other serially connected energy storage cells. One adverse consequence, for example, involves the voltage of an anomalous energy storage cell within the series string, which can rapidly exceed a nominal maximum voltage limit during charging. Such an overvoltage or overcharge condition may damage the cell and significantly reduce the service life of the cell and other cells within the series connection.
It can be appreciated that the characteristics of mass manufactured energy storage cells will deviate to varying degrees from a given set of requirements. Further, cell characteristics, even if considered acceptable at the time of manufacture, will deviate from manufactured specifications at varying rates over time. In order to detect subtle and pronounced differences in cell chemistry and performance of a series string of modules or cells that constitute a distributed battery system, a comprehensive data acquisition scheme is needed to acquire sufficient information concerning individual module and cell operating conditions. Once acquired, this information must be processed and a corrective action strategy implemented to address anomalous operating conditions that arise in the distributed battery system.
There is a need in the battery manufacturing industry for an apparatus and method for orchestrating the operation of a number of individual series connected energy storing modules and cells, and for implementing a corrective action strategy to remedy faults occurring within the series connected modules and cells. There exists a further need for a distributed battery system that provides for safe and reliable operation in the presence of faults occurring within the battery system. The present invention fulfills these and other needs.